The present invention relates to optical communication systems, and more particularly to systems and methods for monitoring performance of optical communication links.
Increasingly, very high data long distance rate communication links are being implemented using purely optical technology where optical signals are passed over very long distances without the need to recover data and regenerate the optical signal. Such implementations include so-called long haul (LH) systems where optical signals travel on the order of 500 km without regeneration and even ultra-long haul (ULH) where optical signals travel more than 2000 km without regeneration. Further augmenting the data carrying capability and general utility of such optical systems is the use of wave division multiplexing (WDM) and dense wave division multiplexing (DWDM) techniques where multiple signals with different wavelengths share the same fiber.
Reliability in such long haul and ultra long haul optical communication links is imperative. The links carry a very heavy volume of data serving numerous subscribers. Any failure will disrupt their data communications and furthermore potentially impact the revenue of the service provider operating the link. Failure of the described communication link can occur due to, e.g., accidental cutting of the line due to carelessness in digging, impairment of the performance of an intermediate optical amplifier, etc. When such a link is down for any reason, it is very important to locate the fault as quickly as possible so that service may be restored. However, simply monitoring the output of a long haul or ultra long haul link is insufficient to locate the fault along the all-optical route. The fault could be anywhere along hundreds or even thousands of kilometers of optical fiber. Sending trained personnel and appropriate test equipment to make measurements along such a long link is extremely expensive and time consuming.
What is needed are systems and methods for rapidly and conveniently locating transmission faults in long haul and ultra long haul optical communication systems.